The interaction of actin and myosin is responsible for force production in cardiac muscle, as in all muscles. It is important to understand, on a molecular level, the function of normal cardiac myosin so as to define a baseline for possible disease states. We are studying the structure and function of cardiac myosin in two systems. The first system involves the study of canine cardiac myosin. Antibodies prepared against a peptide derived from the hinge portion of the S2 region of this myosin completely blocks translocation of actin by myosin in an in vitro motility assay. This suggests a potential role for S2 in force production. Similarly, an antibody against a light chain subunit (LC1) also inhibits motility. The second system involves studies of normal human cardiac myosin and myosin purified from patients suffering from familial hypertrophic cardiomyopathy. Two families have been identified that have different point mutations in their beta cardiac myosin heavy chain. We have purified myosin from surgical samples derived from both mutations. At present, we see no difference between the in vitro properties of the myosin derived from either mutant or normal hearts. The assays employed have been the K+-EDTA and calcium ATPase activities as well as the in vitro motility assay. In addition, the abnormal myosins are being compared to normal myosins by SDS and nondenaturing polyacrylamide gel electrophoresis. We are continuing these studies in the hopes of identifying abnormal behavior in the mutated myosins.